28.4Language/Country Codes

The following links document ISO and other language and country code
information:

ISO 639-2

ISO 639 provides two sets of language codes, one as a two-letter code set
(639-1) and another as a three-letter code set (this part of ISO 639) for the
representation of names of languages.
ISO 3166-1

These pages document the country names (official short names in English) in
alphabetical order as given in ISO 3166-1 and the corresponding ISO
3166-1-alpha-2 code elements.
BCP 47 (Best Current Practice), RFC 3066

This document describes a language tag for use in cases where it is desired to
indicate the language used in an information object, how to register values for
use in this language tag, and a construct for matching such language
tags.
RFC 3282 (Standards Track)

This document defines a "Content-language:" header, for use in cases where
one desires to indicate the language of something that has RFC 822-like
headers, like MIME body parts or Web documents, and an "Accept-Language:"
header for use in cases where one wishes to indicate one’s preferences with
regard to language.